The invention generally relates to the field of laser imaging printing plates on a platesetter or imaging film on an imagesetter.
The process of transferring text and/or graphic information from electronic form to visual form on an imagable medium is called imaging. The information can be transferred to an imagable media using light such as produced by a laser beam or beams. The imagable media may be a printing plate or film that is sensitive to the wavelength, and/or thermal characteristics of the laser beam(s) used to accomplish imaging.
Some printing plates are imaged using an ablative process where an outer emulsion layer of the plate is removed using a laser beam having very high optical power. Other types of printing plates are thermally sensitive wherein an outer emulsion layer is not removed but is simply exposed to the laser beam also requiring a significantly high power laser beam.
Lasers are known low efficiency devices that require a large amount of input electrical power in order to provide modest levels of output optical power. The difference between the amount of electrical power provided to the laser and the output optical power generated by the laser is dissipated as heat. Proper operation of the laser requires removing the excess heat produced by the laser. Failure to remove excess heat from the laser can lead to the laser not meeting performance specifications. Consequently, an imageable media will not be properly exposed yielding a defective product wherein the image is not completely transferred to the plate, or the image is distorted. Even worse, failure to remove the excess heat from the laser can result in premature failure of the laser as is well known in the industry. Consequently, adequate means must be provided to remove excess heat from the laser.
Other components of a laser imaging system such as a laser power supply and laser light valve also require cooling. The laser power supply is used to provide electrical power to the laser. The power supply is also not 100 percent efficient resulting in significant heat being generated within the power supply that must be removed.
The laser light valve is used to produce a plurality of individually controllable laser light beams. Two types of laser light valves are the Grating Light Valve (GLV) produced by Silicon Light Machines, and the DMD micro-mirror light valve by Texas Instruments. Light valves are often supplied with the high optical power from laser sources. Since light valves must handle high power laser beams and also have losses, some of the input optic power supplied by the laser is lost as heat and must be removed from the light valve in order to function properly.
Various components of a laser imaging system present different thermal loads necessitating different degrees of cooling.
Some workers have simply employed separate, dedicated cooling systems for each laser component, each cooling system having unique cooling capabilities.
U.S. Pat. No. 3,569,860 to Booth, and U.S. Pat. No. 5,327,442 to Yarborough et al both teach such a design. Both Booth and Yarborough use separate cooling systems to cool a laser gain medium such as a rod(s), and a flash lamp(s) for pumping the rod(s). This approach, though technically adequate for cooling purposes, is expensive, complex, and requires a large floor space. Further, multiple, separate cooling systems are too bulky to include in an imagesetter or platesetter.
U.S. Pat. No. 5,781,574 to Connors et al teaches a method of cooling a plurality of lasers using a heat exchanger. The system taught by the ""574 patent is effective because Connors teaches using four individual lasers that are pulsed on and off at a low duty cycle and xe2x80x9caddingxe2x80x9d the output beams together into a single beam. This prevents generation of large amounts of heat at a significant increase in cost, complexity, and shear volume of parts. With such little heat generated in this manner, a simple heat exchanger may be employed as taught by Connors to cool the plurality of lasers.
Other attempts to cool multiple laser components (e.g. laser rod, and/or laser flash lamp) presenting different thermal loads, use a single cooling system, but require insulating a laser component from the coolant as described in U.S. Pat. No. 5,848,081 to Reed et al. This technique applies a portion of the cooling capacity of a cooling system to an insulated laser rod, while allowing for the application of the remaining cooling capacity to an uninsulated flash lamp.
A similar method taught by Hill et al in U.S. Pat. No. 4,096,450 uses two separate cooling systems where one cooling system cools a flashlamp via conduction by surrounding a portion of the lamp with barium sulfate powder. The other system cools a laser rod by circulating coolant around the rod.
Problems described in the prior art supra, and others, are solved by applicant""s invention of providing a single cooling system capable of cooling not only a laser and the laser components, but the system level components in the laser imaging system including the laser power supply and laser light valve. Further, the cooling system is capable of cooling components of a laser imaging system that present different thermal loads to the cooling system.
An object of the invention herein is to provide a single cooling system capable of cooling a laser, a laser power supply, and a laser light valve simultaneously.
A further object of the invention herein is to provide a single cooling system capable of cooling multiple thermal loads requiring different degrees of cooling.
A further object of the invention herein is to provide a single cooling system that precludes premature laser failure due to overheating of the laser.
Another object of the invention is to provide thermal protection for a laser in the event a coolant flow problem arises in any portion of the cooling system.